1. Field of the Invention
This invention relates to an electrodeless lamp which generates bright white emission from an oxygen containing plasma in contact with metal atoms such as molybdenum or tungsten.
2. Description of the Related Art
In spite of the large variety of lighting technologies available in the marketplace, there is still a need for efficient, large area illumination sources. At this time, there are two major forms of commercial light sources, filament lamps and discharge lamps. Within the discharge lamp classification, there are two sub categories of electroded (arc) and non-electroded lamps.
The essential advantages associated with the traditional incandescent (filament) lamp are the excellent color rendering indices produced by the hot filament. However, the superior color balance is obtained at the expense of the luminous efficiency. Since the filament essentially acts as a black body radiator at 2500-3000.degree. C., most of the radiant energy is expended in the form of infrared radiation, which is undetectable to the human eye. Furthermore, the large output of IR radiation introduces an additional engineering complexity with respect to the lamp housing in the form of special dichroic coatings that selectively reflect or transmit visible light. Another significant limitation of filament lamps is associated with operational lifetime due to thermal erosion of the filament. The addition of halogens to the inert gas fill has certainly extended the lifetimes of the filament through catalytic cycling of the metal from the walls. However, failure ultimately occurs from re-deposition of filament material to cooler spots in the lamp. Finally, since the hot filament is spatially very small, the lamps act primarily as point sources. Therefore, illuminating large areas becomes problematic and inefficient, and arrays of bulbs are generally employed.
Electrode discharge lamps, such as traditional fluorescent lighting, suffer from the same problem of electrode erosion as filament lamps. To make matters worse, these lamps employ mercury vapor as the primary emitter. Mercury has known toxic effects on humans, and it is considered a severe environmental pollutant. Therefore, it is anticipated that future disposal problems will only become worse as population pressures intensify in urban and suburban areas. Mercury emits radiation in distinct lines, the strongest of which lie in the ultraviolet (UV) at 254 nm. Hence, the color rendering of most mercury-based lamps is enhanced by coating the inside of the glass bulbs with a phosphor, which absorbs the UV and re-emits in the visible spectrum. While this technology improves the color balance, the quantum efficiency of the phosphor is near unity, so that one UV photon is converted to one visible photon and heat. Thus, energy efficiency is compromised. Finally, the phosphors themselves are composed of rare earths and may pose potential environmental remediation problems.
One modification of the discharge lamp that alleviates electrode failure is to inductively couple the power into the working gas. Most of these commercial electrodeless lamps still rely on mercury based chemistries and continue to suffer from all the same limitations described above. One notable exception is a sulfur based illumination source. This lamp has excellent color balance and good efficiency, however it operates as a compressed discharge at high pressure and power density. Consequently, the lamp demands active cooling. As a point source it is akin to the filament lamp, and, hence, poor for large area lighting. The technological solution that has been employed in the art is to fabricate light pipes, which degrade the illumination due to transmission losses.
3. Objects of the Invention
It is an object of this invention to provide a discharge lamp which contains no mercury.
It is a further object of this invention to provide a discharge lamp which contains no active electrode.
It is a further object of this invention to provide a discharge lamp which is environmentally safe and less toxic to humans.
It is a further object of this invention to provide a discharge lamp which uses inductively coupled radio frequency power.
It is a further object of this invention to provide a discharge lamp which operates at low pressure.
It is a further object of this invention to provide a discharge lamp which is an extended illumination source.
It is a further object of this invention to provide a discharge lamp which has improved color balance.
It is a further object of this invention to provide a discharge lamp which has improved luminous efficiency.
It is a further object of this invention to provide a discharge lamp which scales to large area.
It is a further object of this invention to provide a discharge lamp which does not require any phosphors.
It is a further object of this invention to provide a discharge lamp which uses a gas source that is very inexpensive.
These and further objects of the invention will become apparent as the description of the invention proceeds.